Re: [PATCH] drm/xe: Create LRC BO without VM

[Matthew Brost <matthew.brost@intel.com>]

On Wed, May 28, 2025 at 09:04:49PM -0700, Niranjana Vishwanathapura wrote:
> Specifying VM during lrc->bo creation requires VM's reference
> to be held for the lifetime of lrc->bo as it will use VM's dma
> reservation object. Using VM's dma reservation object for
> lrc->bo doesn't provide any advantage. Hence do not pass VM
> while creating lrc->bo.
> 
> Fixes: 264eecdba211 ("drm/xe: Decouple xe_exec_queue and xe_lrc")
> Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>

Good cleanup. I thought this through and can't reason why this would
work or any advantages of the LRC using VM's dma-resv. 

One nit, xe_lrc_finish can use xe_bo_unpin_map_no_vm on lrc->bo now.

Asssuming CI passes and the above nit fixed:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/xe/xe_exec_queue.c |  9 ---------
>  drivers/gpu/drm/xe/xe_lrc.c        | 18 +++---------------
>  2 files changed, 3 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
> index ce78cee5dec6..32c6923df7c3 100644
> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
> @@ -132,12 +132,6 @@ static int __xe_exec_queue_init(struct xe_exec_queue *q)
>  			flags |= XE_LRC_CREATE_RUNALONE;
>  	}
>  
> -	if (vm) {
> -		err = xe_vm_lock(vm, true);
> -		if (err)
> -			return err;
> -	}
> -
>  	for (i = 0; i < q->width; ++i) {
>  		q->lrc[i] = xe_lrc_create(q->hwe, q->vm, SZ_16K, q->msix_vec, flags);
>  		if (IS_ERR(q->lrc[i])) {
> @@ -146,9 +140,6 @@ static int __xe_exec_queue_init(struct xe_exec_queue *q)
>  		}
>  	}
>  
> -	if (vm)
> -		xe_vm_unlock(vm);
> -
>  	err = q->ops->init(q);
>  	if (err)
>  		goto err_lrc;
> diff --git a/drivers/gpu/drm/xe/xe_lrc.c b/drivers/gpu/drm/xe/xe_lrc.c
> index 61a2e87990a9..974fe509df0e 100644
> --- a/drivers/gpu/drm/xe/xe_lrc.c
> +++ b/drivers/gpu/drm/xe/xe_lrc.c
> @@ -1007,7 +1007,7 @@ static int xe_lrc_init(struct xe_lrc *lrc, struct xe_hw_engine *hwe,
>  	 * FIXME: Perma-pinning LRC as we don't yet support moving GGTT address
>  	 * via VM bind calls.
>  	 */
> -	lrc->bo = xe_bo_create_pin_map(xe, tile, vm, lrc_size,
> +	lrc->bo = xe_bo_create_pin_map(xe, tile, NULL, lrc_size,
>  				       ttm_bo_type_kernel,
>  				       bo_flags);
>  	if (IS_ERR(lrc->bo))
> @@ -1795,9 +1795,6 @@ struct xe_lrc_snapshot *xe_lrc_snapshot_capture(struct xe_lrc *lrc)
>  	if (!snapshot)
>  		return NULL;
>  
> -	if (lrc->bo->vm)
> -		xe_vm_get(lrc->bo->vm);
> -
>  	snapshot->context_desc = xe_lrc_ggtt_addr(lrc);
>  	snapshot->ring_addr = __xe_lrc_ring_ggtt_addr(lrc);
>  	snapshot->indirect_context_desc = xe_lrc_indirect_ring_ggtt_addr(lrc);
> @@ -1819,14 +1816,12 @@ struct xe_lrc_snapshot *xe_lrc_snapshot_capture(struct xe_lrc *lrc)
>  void xe_lrc_snapshot_capture_delayed(struct xe_lrc_snapshot *snapshot)
>  {
>  	struct xe_bo *bo;
> -	struct xe_vm *vm;
>  	struct iosys_map src;
>  
>  	if (!snapshot)
>  		return;
>  
>  	bo = snapshot->lrc_bo;
> -	vm = bo->vm;
>  	snapshot->lrc_bo = NULL;
>  
>  	snapshot->lrc_snapshot = kvmalloc(snapshot->lrc_size, GFP_KERNEL);
> @@ -1846,8 +1841,6 @@ void xe_lrc_snapshot_capture_delayed(struct xe_lrc_snapshot *snapshot)
>  	xe_bo_unlock(bo);
>  put_bo:
>  	xe_bo_put(bo);
> -	if (vm)
> -		xe_vm_put(vm);
>  }
>  
>  void xe_lrc_snapshot_print(struct xe_lrc_snapshot *snapshot, struct drm_printer *p)
> @@ -1900,14 +1893,9 @@ void xe_lrc_snapshot_free(struct xe_lrc_snapshot *snapshot)
>  		return;
>  
>  	kvfree(snapshot->lrc_snapshot);
> -	if (snapshot->lrc_bo) {
> -		struct xe_vm *vm;
> -
> -		vm = snapshot->lrc_bo->vm;
> +	if (snapshot->lrc_bo)
>  		xe_bo_put(snapshot->lrc_bo);
> -		if (vm)
> -			xe_vm_put(vm);
> -	}
> +
>  	kfree(snapshot);
>  }
>  
> -- 
> 2.43.0
>